asio C++ library Files

The asio 1.4.6 release continues the 1.4.x stable release series.

The changes in this release include:

* Reduced compile times. (Note that some programs may need to add additional
  #includes, e.g. if the program uses boost::array but does not explicitly
  include <boost/array.hpp>.)

* Reduced the size of generated code.

* Refactored deadline_timer implementation to improve performance.

* Improved multiprocessor scalability on Windows by using a dedicated hidden
  thread to wait for timers.

* Improved performance of asio::streambuf with async_read() and 
  async_read_until(). These read operations now use the existing capacity of
  the streambuf when reading, rather than limiting the read to 512 bytes.

* Added optional separate compilation. To enable, include
  asio/impl/src.cpp in one source file in a program, then
  build the program with (BOOST_)ASIO_SEPARATE_COMPILATION defined in the
  project\/compiler settings. Alternatively, (BOOST_)ASIO_DYN_LINK may be
  defined to build a separately-compiled Asio as part of a shared library.

* Added new macro (BOOST_)ASIO_DISABLE_FENCED_BLOCK to permit the disabling of
  memory fences around completion handlers, even if thread support is enabled.

* Reworked timeout examples to better illustrate typical use cases.

* Ensured that handler arguments are passed as const types.

* Fixed incorrect parameter order in null_buffers variant of async_send_to.

* Ensured unsigned char is used with isdigit in getaddrinfo emulation.

* Fixed handling of very small but non-zero timeouts.

* Fixed crash that occurred when an empty buffer sequence was passed to a
  composed read or write operation.

* Added missing operator+ overload in buffers_iterator.
  
* Implemented cancellation of null_buffers operations on Windows.